Structural determinants of opioid activity in derivatives of 14-aminomorphinones: Effects of changes to the chain linking of the C ₁₄-amino group to the aryl ring

The 14-aminodihydromorphinone and codeinone series of opioid ligands have produced a number of ligands of substantial interest. To investigate the importance of the 14-substituent, a series of analogues in which the side chain length is varied and the amide and alkene functions are reduced have been prepared. Binding affinity, particularly at the μ-opioid receptor (MOR), was largely determined by the aromatic group of the side chain. In the [ ³⁵S]GTPγS functional assay, the ligands having a three-carbon side chain were more potent antagonists than their longer chain counterparts, while shorter, two-carbon chain analogues were of higher MOR efficacy, an effect that was confirmed in vivo. Wash-resistant binding was observed within this series and appeared to be unrelated to side-chain length.